Organic light emitting diode (OLED) is one of the hot spots in the research of flat panel display today. Compared with liquid crystal display, the OLED display device has the advantages of low energy consumption, low production cost, self luminous, wide viewing angle, quick response and so on. At present, in the flat panel display field of mobile phone, PDA, digital cameras and so on, OLED display device has begun to replace the traditional liquid crystal display (LCD).
The structure of an OLED display device mainly comprises: a basal substrate, and pixels arranged in a matrix formed on the basal substrate. Wherein the pixels are organic electroluminescent structures typically formed at corresponding pixel positions in an array substrate with organic material, by applying evaporation film technology through a high precision metal mask plate. In order to perform color display, an OLED display should be colorized. The best color image effect can be achieved with a side-by-side arrangement. The side-by-side arrangement refers to three sub pixels of red, green, blue (G, R, B) arranged in a range of one pixel, each sub pixel has a separate organic electroluminescent structure. due to the difference in the organic electroluminescent materials of red, green and blue sub pixels, in the production process, a metal mask plate is required for evaporation of three different organic electroluminescent materials for the red, green and blue sub-pixels (of three primary colors) at corresponding positions, and then adjust the color blending of these three colors, realizing true color.
The key point for manufacturing OLED display device with high resolution (PPI) is high precise metal mask plate, which is precise and has a good mechanical stability; while the key point for high precise metal mask plate lies in the arrangement of pixels and sub pixels.
Currently, in an existing OLED display device, the arrangement of the pixel array is typically a side-by-side arrangement. As shown in FIG. 1, the OLED display device comprises a basal substrate 1, and pixel units 2 arranged in an array on the basal substrate 1; a pixel unit 2 comprises three parallel sub pixels of red (R), green (G), and blue (B). In order to form the arrangement of the pixel, a corresponding metal mask plate is shown in FIG. 2. FIG. 2 schematically shows a metal mask plate used for forming a sub pixel (R sub pixel) in the pixel arrangement shown in FIG. 1. Since the patterns of the sub pixels are the same, a metal mask plate with the same structure can be used to form other sub pixels (B).
In FIG. 2, a metal mask plate comprises a metal substrate 3 and rectangular openings 4 on the metal substrate 3. Since the sub pixels in a same column in the display device share a same opening, the length of the opening 4 in the metal mask plate is long. For low resolution display device, since the number of pixels is small, the width of the metal strip between adjacent openings 4 on the metal mask plate is wide; therefore the production, application and management of such metal mask plates is simple. However, with the increase of the display resolution, the width of the metal strip between adjacent openings in the metal mask plate is smaller, which causes that the metal strip between adjacent openings in the metal mask plate is easily deformed by external influence during the using process, resulting in color mixing due to the cross contamination of the organic electroluminescent materials with different colors in the sub pixels, causing a low yield rate of the product.
In view of the above problems, a metal mask plate shown in FIG. 3 is proposed, to form a pixel arrangement as shown in FIG. 1. As shown in FIG. 3, the metal mask plate is provided by adding metal lapping bridges 5 at positions between adjacent sub pixels shown in FIG. 1 to the metal mask plate as shown in FIG. 2, to connect adjacent metal strips, modifying a opening 4 shown in FIG. 2 into openings 6 corresponding to the sub pixels shown in FIG. 1. Although the method can make the shape of the metal strips in the metal mask plate more stable, in order to avoid masking effect of the metal lapping bridges to the sub pixels, a sufficient distance should be kept between the sub pixels and the metal lapping bridges, which can reduce the size of the sub pixels, thus affecting the opening rate of the OLED display device.